In regard to compositions containing a substance which is likely to deteriorate under the neutral or alkaline condition, a technique in which an acidic substance as a pH adjuster is made to be contained in the composition to generate such a pH environment that can suppress its deterioration has been known, and in regard to compositions containing a substance which is slightly soluble under the neutral or alkaline condition, a technique in which an acidic substance as a pH adjuster is made to be contained in the composition to generate such a pH environment that can improve its solubility has been known (Patent Literature 1).
Patent Literature 1: WO 03/055525